There is a wheel-slip detection system shown and described in Japanese Pat. No. 57-55001, which is a prior type of method for detecting wheel-slip. This patent relates to the detection of the speeds of all the wheels and the selection of the one with the highest speed to establish the basic speed reference to which the speeds of the various wheels are compared to determine the speed differential, or to determine the differential value of said speed differentials or differentiating the various wheels of said wheels to obtain the reduced speeds. When these various speed differentials, the various differential values, or the various reduced speeds exceed the set value, this unit determines that skidding of the wheels is occurring in this method. This skidding information is transmitted to the braking system, and is used to control the braking force applied to the wheels of the car.
In the case of railroad vehicle wheels, even when said braking force is not decreased, there are times when the slipping condition is dissipated naturally in a "resticking viscous sticking phenomenon" or self-readhesion. This phenomenon, or effect, shortens the controlling distance so that it is something which should be utilized as much as possible.
The prior art method of accomplishing the above results is by making the set value higher than a certain selected value and expanding the relative spread of the insensitive width, so that it is possible to detect a smaller slipping condition if the above-mentioned method was employed.
On the other hand, when all of the wheels of the car have almost the same small skidding values, the wheel which serves as the basic wheel is in a skidding situation, and the speed differential of the various wheels with respect to the basic speed or the differential speeds of said speed differential are small, or when the speeds of each wheel are differentiated in order to yield a small differential speed. The method of the prior art in which the set value is in the insensitive zone was made large and the small slips, hereafter called "sluggish slip", cannot be detected, no matter how long it takes. It will be appreciated that in the worst possible case, when all the wheels of the car become locked and the control distance to be extended causes damage to the outer rims of the wheels, namely, causing flat spots on the wheels, become a problem.